This invention relates to a corrugated waveguide, suitable for use in a satellite communication system and, more particularly, to a form of corrugation reducing power loss associated with penetration of a waveguide wall by electromagnetic fields.
Flexible waveguides are employed for interconnecting electronic components, such as microwave components carried by a satellite in a satellite communications system. A common form of flexible waveguide has steps and/or corrugations which permit a flexing of the waveguide while facilitating its manufacture. In the usual construction of such a waveguide, ends of the waveguide are provided with flanges by which the waveguide can be secured to the electronic components which are to be interconnected. The flexibility of the waveguide permits the flanges to be moved about and oriented for attachment to the electronic components.
A desirable feature in such a waveguide is the minimization of loss of power for electromagnetic waves transmitted via the waveguide. The internal geometry of available flexible waveguides having steps and relatively sharp-cornered corrugations is not designed to be optimal from the point of view of reducing power loss. Therefore, the available flexible waveguides present the disadvantage of unnecessarily large power loss in the communication of electromagnetic waves between microwave components.
The aforementioned disadvantage is overcome and other benefits are provided by a flexible waveguide, wherein flexibility is provided by corrugations constructed in accordance with the invention with a rounded or sinuous form. The corrugations need be provided only on the inside of the waveguide. However, as a convenience in the manufacture of the waveguide of thin sheet material, the sheet material may be bent in a manner wherein the corrugations appear on both the inside and the outside of the waveguide. The distance between corrugations should be significantly less than the wavelength, preferably less than approximately 0.2 wavelength of the electromagnetic radiation carried by the waveguide. The height (or depth) of a corrugation is less than approximately 0.5 wavelength but is greater than the distance between the corrugations.
In the theory of operation of the invention, the corrugations, with the cross-sectional dimensions substantially smaller than a wavelength, may be likened to an electrically conductive wall with small holes therein. The holes have cross-sectional dimensions substantially less than a wavelength. In such an electromagnetic structure, there is little penetration of electromagnetic energy through the holes with the result that an electromagnetic wave interacting with the wall interacts with a reduced surface region of the wall. By way of example of such interaction, a component of the magnetic vector parallel to the surface of the wall may induce a surface current in the wall resulting in a power loss proportional to the product of the current and resistance of the wall. The presence of numerous small holes in the wall reduces the amount of wall surface available for interaction with the electromagnetic wave, with a consequent reduction in the amount of power loss. In similar fashion, the presence of the corrugations reduces the amount of surface current and the power loss associated therewith. Performance of the waveguide is improved by the use of the corrugations, the performance being characterized by reduced power loss and insignificant generation of higher order modes of the electromagnetic wave.